Friction false twist devices of this type are wellknown, generally comprising three rotatable shafts, each being provided with at least one rotationally symmetric friction element. A top view of the three shafts shows they form the corners of an equilateral triangle when in their operating or working positions, the shafts being individually adjustable, and the yarn to be false-twisted running between the friction elements. The three shafts can be shifted individually or collectively from their working positions into threading-up positions, as shown in German AS No. 2 213 147, correspondng to British Pat. No. 1,376,272. Each of the three shafts can be provided with a whorl, one of the shafts being coupled to a drive motor, and the others indirectly driven through an elastic O-ring linking all whorls. Another well-known device is driven through gears mounted on the shafts and meshing with cogged belts, as shown in Swiss Pat. No. 591,578, corresponding to U.S. Pat. No. 3,932,985. In the device of this latter patent, the belt is actually driven by a fourth shaft, the cogged belt passing around gears on each of the four shafts.
I consider that the disadvantage of the elastic and cogged belts is that they are not well-suited to the very high speeds that are required for modern false-twist friction texturing devices. For instance, with elastic belts, power transmission frequently is not constant in time, slippage is caused by stretch, and service life can be very limited. With cogged belts, relatively small gears, with correspondingly fine pitch, must be employed owing to space limitations. A relatively high belt tension must also be selected, sometimes at the expense of achieving continuous precision meshing of belt and gears.
The object of the present invention is to avoid some or all of the aforementioned shortcomings by providing a drive for the individual shafts of a friction false-twist texturing device of the type described above, which is of relatively simple design, and at the same time serves to transmit torque reliably.
In general, these objects are met in the preferred embodiments of the invention by the incorporation of an additional shaft provided with a whorl and arranged in relation to the shafts carrying the friction elements so that lines connecting the centers of the four shafts preferably form a kite-shaped quadrilateral, with one pair of opposing shafts capable of shifting in relation to the other pair between working and threading-up positions, and with an endless belt of minimum elasticity linking the whorls of all shafts.
The advantage of this preferred solution is that the relative shifting of either pair of opposing shafts forming the kite-shaped quadrilateral for the purpose of threading-up calls for only a minimum modification of the belt length, if any. Thus, this feature permits the use of belts having minimum elasticity and support structure, thereby assuring that the power transmission is constant over a given period of time, and that service life of the belt is extended, even at very high speeds. While this is the preferred arrangement, the basic principal is to arrange the shiftable shafts such that any belt lengthening tendency upon the shifting of one shaft is substantially compensated by the conjoint shifting of the other shaft, in combination with the overall configuration of the shaft centers and the belt path. In the preferred arrangements, the configuration formed by the shafts and the selection of the movable shafts and their directions of movement are such that any belt-lengthening tendency stemming from the movement of one of the movable shafts is minimized.
Preferably a pair of shafts carrying friction elements at opposite corners of the kite-shaped quadrilateral are shifted in relation to the other pair of shafts, which may be fixed. The additional shaft can be either parallel or vertical to the shafts carrying the friction elements, the vertical application involving the use of guide rolls between the whorls.